The present invention relates to a recording and/or reproducing apparatus, a recording and/or reproducing method, a recording medium and a program. To be more specific, the present invention relates to a recording and/or reproducing apparatus for tape-shaped recording medium. Even more particularly, the present invention relates to a recording and/or reproducing apparatus, which are provided for tape-shaped recording medium each made of a magnetic recording medium having an anisotropic property oblique with respect to the thickness direction.
In general, a linear tape streamer and a helical scan tape streamer are known as the conventional tape streamer. In a linear tape streamer, when data is recorded on a tape-shaped magnetic recording medium, an initial recording track parallel to the tape traveling direction (or the longitudinal direction) of the tape is created by using a fixed magnetic head. As the recording position arrives at one end of the tape, the traveling direction of the tape is reversed to record data along another track adjacent to the initial recording track and thereby forming a recording track. This operation is repeated alternately to record data onto the magnetic recording tape. Such a linear tape streamer conforms to a variety of formats such as the QIC (Quarter Inch Cartridge: a trademark), the DLT (Digital Linear Tape: a trademark) and the IBM 3480 (a trademark) provided by IBM.
In each of these linear magnetic recording apparatus, normally, an induction ring head is employed as a head for writing a signal onto a tape-shaped magnetic recording medium but, as a head for reading out a signal from the recording medium, the induction ring head or a magneto resistance effect head (an MR head) can be used. As the tape-shaped magnetic recording medium, a coated magnetic tape is used. Examples of the coated magnetic tape are an FeCoNi metallic alloy tape and an Fe-oxide tape with magnetic particles thereof oriented in the longitudinal direction.
A coated magnetic tape with its magnetism oriented in the longitudinal direction is used because, by orienting the magnetism uniformly in the same direction, the amount of residual magnetization and the aquareness ratio are improved so that the TAA (Time Average Amplitude) and spatial resolution PW (Pulse Width) 50 of a recording and/or reproducing signal are increased at the same time. Thus, the use of such a coated magnetic tape results in merits of an enhanced signal-to-noise ratio and, hence, an improved recording density. If a coated magnetic tape is used, the magnetism is oriented in the longitudinal direction. Therefore, a coated magnetic tape is used because there is no resulting difference in recording and reproducing characteristics between the two tape traveling directions when the magnetic tape is traveling back and forth.
In a helical scan tape streamer, on the other hand, a magnetic head is provided on a cylinder drum, which is rotating at a high speed. A tape-shaped magnetic recording medium is wound in an inclined direction on the cylinder drum. When the tape-shaped magnetic recording medium is traveling in one direction, data is recorded onto the magnetic recording medium. Such a helical scan tape streamer conforms to a variety of formats such as the DDS (Digital Data Storage) based on the DAT (Digital Audio Tape) technology, the AIT (Advance Intelligent Tape) based on an 8-mm video technology and the DTF (Digital Tape Format) based on a ½-inch tape technology developed for broadcasting stations.
In each of these helical scan tape streamers, a recording track is sequentially formed slantingly with respect to the traveling direction of the tape. That is to say, a signal is recorded in a one direction from the winding start of the tape to the winding end thereof but, unlike the linear tape streamer, back-and-forth recording is not carried out.
In recent years, there have been introduced helical scan tape streamers having formats for specially increasing the recording density. Examples of such formats are the AIT (Advance Intelligent Tape) format and the DVC (Digital Video Cassette) format for consumer applications. Such helical scan tape streamers each employ an evaporation tape, which has an oblique anisotropic property, as a tape-shaped magnetic recording medium. An evaporation tape is created by heating a ferromagnetic metal such as CoFe in a vacuum to a high temperature till the metal evaporates, directly forming a magnetic layer on a base film. Since such a tape does not include an organic binder, the magnetic material filling density is high, giving rise to an excellent magnetic characteristic and widely known possibility of recording operations at a high recording density.
An evaporation tape exhibits recording and/or reproducing characteristics varying in dependence on the direction, in which a magnetic head writes a signal onto the tape due to, among other causes, an oblique anisotropic property attributed to the actual mechanism of the magnetic material. For this reason, an evaporation tape is generally used only in one traveling direction resulting in a high spatial resolution PW50. This direction is normally referred to as a forward traveling direction. It is to be noted that the oblique anisotropic property is not a characteristic inherent only in an evaporation tape.
If an oriented magnetic field is applied in the traversal direction of a coated magnetic tape after an oriented magnetic field has been once applied in the longitudinal direction of the tape, for example, the tape will exhibit an oblique anisotropic property, which allows the recording and/or reproducing characteristics of a short-wave signal to be improved. However, differences in recording and/or reproducing characteristics between the traveling directions, that is, between forward and reversed directions, have been reported in a document with a title of “Metal Tapes for High-Band 8 mm” authored by Tsukidate et al. and presented to a national conference of the Institute of Television Engineers in the year of 1989.
If a tape-shaped magnetic recording medium is used in a helical scan tape streamer, the oblique anisotropic property of the tape-shaped magnetic recording medium raises no big problems because the tape can be transferred in such a way that a signal is recorded in one direction from the winding start of the tape to the winding end thereof as described above, that is, in only the forward direction, which exhibits an excellent magnetic conversion characteristic.
If a tape-shaped magnetic recording medium is used in a linear tape streamer, however, back-and-forth recording operations must be carried out. The magnetic conversion characteristic in the reversed direction, which is a direction not used in a helical scan tape streamer, is also required to almost the same degree as the forward direction. Thus, it is extremely difficult to improve the recording density in a linear tape streamer using a magnetic recording medium having an oblique anisotropic property.
In order to solve the problem described above, there has been reported an experiment to eliminate the differences in recording and reproducing characteristics between the forward and reversed directions by, typically, forming two magnetic layers on the magnetic recording medium and making the orientation of the anisotropic property on one of the magnetic layers opposite to the orientation of the anisotropic property on the other magnetic layer. The experiment is disclosed in references such as a document authored by Himeno et al. with a title of “Recording Signals on a Magnetic Tape Having a High Recording Density by Adoption of a Non-Tracking Method” in a magazine of the Institute of Electronic and Communication Engineers C-II Vol. J75-C-II No. 11 1992 and Japanese Patent Laid-open No. Hei 11-328645. In accordance with this magnetic recording method, however, the magnetic recording medium has a two-layer structure comprising two magnetic layers, that is, an upper layer and a lower layer wherein the orientation of the anisotropic property on one of the magnetic layers is opposite to the orientation of the anisotropic property on the other magnetic layer. Thus, there is raised a problem that it is feared that the recording and reproducing characteristics, particularly, the spatial resolution (PW50) unavoidably deteriorate so that the process to manufacture the magnetic recording medium inevitably becomes complicated, causing poorer producibility of the recording medium.
In consequence, the linear tape streamer has a problem that it is extremely difficult to increase the recording density by using a magnetic recording medium exhibiting an oblique anisotropic property.
In order to solve this problem, Japanese Patent Laid-open No. Hei 5-67374 proposes an improvement of a reproducing characteristic by varying coefficients of an equivalent circuit for a reproducing apparatus in which there are different tape traveling directions. An attempt has also been made to eliminate differences in recording and reproducing characteristics between the forward and reversed directions by forming two magnetic layers on the magnetic recording medium and making the orientation of the anisotropic property on one of the magnetic layers opposite to the orientation of the anisotropic property on the other magnetic layer.
While Japanese Patent Laid-open No. Hei 5-67374 shows a general design example of a gain-frequency characteristic used as a characteristic of an waveform equalizer, an object of design of the equalizer with respect to variations in magnetic conversion system, particularly, a detailed description and an object of design of a phase frequency characteristic is not described in concrete terms. In accordance with results of intensive researches conducted one after another on recording and/or reproducing apparatus using a recording medium having an oblique anisotropic property by the inventors of the present invention, there is a big difference in phase between the traveling directions of a tape-shaped magnetic recording medium having an oblique anisotropic property. For this reason, it is quite within the bounds of possibility that a sufficient characteristic cannot be obtained even if coefficients of the equivalent circuit are changed in accordance with the general design example unless the phase equalization is also taken into consideration in addition to the waveform equalization as described in Japanese Patent Laid-open No. Hei 5-67374. If the phase equalization is not carried out in an analog equalizer in every direction, it is quite within the bounds of possibility that the operation of a PLL (Phase Locked Loop) employed in an ADC (Analog-to-Digital Converter) hardly works.
While Japanese Patent Laid-open No. Hei 5-67374 discloses a data reproducing apparatus carrying out an adaptive equalization process, consideration of a characteristic of a recording medium having an oblique anisotropic property at a recording time is not described.